Investigations of connections for precast concrete panel buildings have shown that it is difficult to design an embedded connection that will perform well under earthquake loading. Some typical connections use studs or reinforcing bars embedded in the edge of the panel. These are then welded or bolted to an adjacent panel. During earthquake loading the crushing of concrete around the embedment usually leads to premature loss of strength and stiffness of the connection before significant ductility can develop. It has been found that connection performance improves with increasing panel thickness. The behaviour of embedded connections in thin precast concrete panels was investigated. The intent was to improve connection design details and to develop a simple method of predicting connection strengths with panel thicknesses of 50 mm to 75 mm. Sixteen connections of six different types were tested. Three were tested monotonically and thirteen were tested under reversed cyclic loading. Certain types of connections can be used to transfer earthquake loads between thin concrete panels as long as they have adequate strength. Methods for predicting the strength of connections are discussed. The connections tested should not be relied on to develop ductility. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Master of Engineering

no abstract provided by author / Master of Engineering

This research investigates the interaction between heavy precast cladding units attached to steel framed buildings. Cladding systems are designed as non-structural components and are not expected to contribute to the energy absorption of the primary structure. However, research has indicated that the cladding system may be designed to reduce the response of the primary structure under seismic excitations. The use of flexible connections between the cladding and primary structural frames may be able to provide beneficial effects to the entire structural response. In this study, a series of earthquake engineering simulations were conducted in OPENSEES to analyze the effects of the flexible connections of the cladding on both a 3 story and 9 story prototype structures. The research focus is on the 3 story structure. The results from 3 story and 9 story structures indicate that the flexible cladding connections have the ability to transfer hysteretic energy from the primary structure to the flexible cladding connections.

Multiple experimental and computational tests are performed on precast concrete structures designed for damage avoidance. These structures accommodate non-linear behaviour by rocking at specially detailed connections. Unbonded prestress is employed to provide a restoring force and supplemental devices are used to dissipate energy. Tests are performed on a 30 percent scale bridge pier and an 80 percent scale 3D beam-column joint subassembly. Several detailing strategies are developed and tested. Straight and draped tendon profiles are considered. Supplemental energy dissipation is provided by yielding mild steel devices or lead-extrusion dampers. The lead-extrusion dampers are tested both externally and internally. Detailing at the joint region is refined in an effort to provide a cost-effective and simple solution. A closure pour is considered to simply the construction process. Results indicate it is possible to eliminate virtually all damage at the beam-column joint with minor increased cost from steel armouring. The lead-extrusion damper is shown to be 'resetable', and therefore would not have to be replaced following a seismic event. Two seismic financial risk methodologies are developed to investigate the enhanced performance inherent to ductile jointed structures. A rapid method is introduced which simplifies the intensive computational effort necessary to perform loss studies. A distribution-free computational method is also examined. The methods are demonstrated with a case study of bridge piers designed to different seismic design codes and a bridge designed for damage avoidance. The bridge pier designed for damage avoidance is shown to have an expected annual loss of approximately 25 percent that of the conventional ductile piers.

Topography effects, the modification of seismic motion by topographic features, have been long recognized to play a key role in elevating seismic risk. Site response, the modification of ground motion by near surface soft soils, has been also shown to strongly affect the amplitude, frequency and duration of seismic motion. Both topography effects and 1-D site response have been extensively studied through field observations, small-scale and field experiments, analytical models and numerical simulations, but each one has been studied independently of the other: studies on topography effects are based on the assumption of a homogeneous elastic halfspace, while 1-D site response studies are almost exclusively formulated for flat earth surface conditions. This thesis investigates the interaction between topographic and soil amplification, focusing on strong ground motions that frequently trigger nonlinear soil response. Recently, a series of centrifuge experiments tested the seismic response of single slopes of various inclination angles at the NEES@UCDavis facility, to investigate the effects of nonlinear soil response on topographic amplification. As part of this collaborative effort, we extended the search space of these experiments using finite element simulations. We first used simulations to determine whether the centrifuge experimental results were representative of free-field conditions. We specifically investigated whether wave reflections caused by the laminar box interfered with mode conversion and wave scattering that govern topographic amplification; and whether this interference was significant enough to qualitatively alter the observed amplification compared to free-field conditions. We found that the laminar box boundaries caused spurious reflections that affected the response near the boundaries; however its effect to the crest-to-free field spectral ratio was found to be insignificant. Most importantly though, we found that the baseplate was instrumental in trapping and amplifying waves scattered and diffracted by the slope, and that in absence of those reflections, topographic amplification would have been negligible. We then used box- and baseplate-free numerical models to study the coupling between topography effects and soil amplification in free-field conditions. Our results showed that the complex wavefield that characterizes the response of topographic features with non-homogeneous soil cannot be predicted by the superposition of topography effects and site response, as is the widespread assumption of engineering and seismological models. We also found that the coupling of soil and topographic amplification occurs both for weak and strong motions, and for pressure-dependent media (Nevada sand), nonlinear soil response further aggravates topographic amplification; we attributed this phenomenon to the reduction of apparent velocity that the low velocity layers suffer during strong ground motion, which intensifies the impedance contrast and accentuates the energy trapping and reverberations in the low strength surficial layers. We finally highlighted the catalytic effects that soil stratigraphy can have in topographic amplification through a case study from the 2010 Haiti Earthquake. Results presented in this thesis imply that topography effects vary significantly with soil stratigraphy, and the two phenomena should be accounted for as a coupled process in seismic code provisions and seismological ground motion predictive models.

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

The purpose of this thesis is to evaluate the seismic response of the UC Physics Building based on recorded ground motions during the Canterbury earthquakes, and to use the recorded response to evaluate the efficacy of various conventional structural analysis modelling assumptions. The recorded instrument data is examined and analysed to determine how the UC Physics Building performed during the earthquake-induced ground motions. Ten of the largest earthquake events from the 2010-11 Canterbury earthquake sequence are selected in order to understand the seismic response under various levels of demand. Peak response amplitude values are found which characterise the demand from each event. Spectral analysis techniques are utilised to find the natural periods of the structure in each orthogonal direction. Significant torsional and rocking responses are also identified from the recorded ground motions. In addition, the observed building response is used to scrutinise the adequacy of NZ design code prescriptions for fundamental period, response spectra, floor acceleration and effective member stiffness. The efficacy of conventional numerical modelling assumptions for representing the UC Physics Building are examined using the observed building response. The numerical models comprise of the following: a one dimensional multi degree of freedom model, a two dimensional model along each axis of the building and a three dimensional model. Both moderate and strong ground motion records are used to examine the response and subsequently clarify the importance of linear and non-linear responses and the inclusion of base flexibility. The effects of soil-structure interaction are found to be significant in the transverse direction but not the longitudinal direction. Non-linear models predict minor in-elastic behaviour in both directions during the 4 September 2010 Mw 7.1 Darfield earthquake. The observed torsional response is found to be accurately captured by the three dimensional model by considering the interaction between the UC Physics Building and the adjacent structure. With the inclusion of adequate numerical modelling assumptions, the structural response is able to be predicted to within 10% for the majority of the earthquake events considered.

A novel stochastic earthquake ground motion model is formulated in association with physically interpretable parameters that are capable of efficiently characterizing the complex evolutionary nature of the phenomenon. A multi-modal, analytical, fully non-stationary spectral version of the Kanai-Tajimi (K-T) model is introduced achieving a realistic description of the evolutionary spectral energy distribution of seismic ground motions. The functional forms describing the temporal evolution of the model parameters can efficiently model highly non-stationary power spectral characteristics. The analysis space, where the analytical forms describing the evolution of the model parameters are established, is the energy domain instead of the typical use of the time domain. This space is used in conjunction with a newly defined energy-associated amplitude modulating function. The Spectral Representation Method supports the simulation of sample ground motions realizations. A predictive stochastic model for simulation of earthquake ground motions is developed, using a user-specified earthquake scenario description as input, and resulting in fully nonstationary ground acceleration time-histories at a site of interest. The previously formed analytical non-stationary K-T ground motion model lies at the core of the developed predictive model. An extensive Californian subset of the NGA-West2 earthquake ground motion database is used to develop and calibrate the predictive stochastic model. Sample observations of the model parameters are obtained by fitting the K-T model to the database records, and their resulting marginal distributions are effectively described by simple probability models. Advanced random-effect regression models are established in the normal probabilistic space, capable of linking the stochastic K-T model parameters with the moment magnitude Mw, closest distance Rrup and average shear-wave velocity VS30 at a Californian site of interest. The included random effects take effectively into account the correlation of ground motions pertaining to the same earthquake event, and the fact that each site is expected to have its own effect on the resulting ground motion. The covariance structure of the normal K-T model parameters is next estimated, allowing finally for the complete mathematical description of the predictive stochastic model for a given earthquake scenario. The entirety of the necessary steps for the simulation of the developed predictive stochastic model is provided, resulting in the generation of any number of fully non-stationary ground acceleration time-series that are statistically consistent with the specified earthquake scenario. In an effort to assess the performance and versatility of the developed predictive stochastic model, a list of simple engineering metrics, associated with the characterization of the earthquake ground motion time-series, is studied, and results from simulated earthquake ground acceleration time-series of the developed predictive model are compared with corresponding predictions of pertinent Ground Motion Prediction Equations (GMPEs) for a variety of earthquake and local-site characteristics. The studied set of ground acceleration time-series features includes the Arias intensity IA, the significant duration T5-95 of the strong ground shaking, and the spectral-based mean period of the earthquake record Tm. The predictive stochastic model is next validated against the state-of-the-art NGA-West2 GMPE models. The statistics of elastic response spectra derived by ensembles of synthetic ground motions are compared with the associated response spectra as predicted by the considered NGA-West2 ground motion prediction equations for a wide spectrum of earthquake scenarios. Finally, earthquake non-linear response-history analyses are conducted for a set of representative single- and multi-degree-of-freedom hysteretic structural systems, comparing the seismically induced inelastic structural demand of the considered systems, when subjected to sets of both real strong ground motion records, and associated simulated ground acceleration time-histories as well. The comparisons are performed in terms of seismic structural demand fragility curves.

Thesis (M.S.)--University of Nevada, Reno, 2004. / "December 2004." Includes bibliographical references (leaves 57-61). Online version available on the World Wide Web.